This invention relates generally to a chain tensioner for chain drives which is particularly, though not exclusively, suitable for use as a tensioner on the timing chain of a motor vehicle engine. The present invention is a chain tensioner particularly suited for use in confined spaces having a flat blade spring element mechanically interlocked with a plastic shoe. The shoe may be of rigid filled nylon and engages the chain to be tensioned.
Conventionally, a blade tensioner is used as the tensioner to apply _tension force onto a chain. One form of prior art blade chain tensioner is shown in U.S. Pat. No. 3,490,302, which is incorporated herein by reference. Another example of a blade tensioner is shown in FIG. 4 and FIG. 5 herein.
As shown in FIG. 4, the conventional blade tensioner 100 is composed of a shoe 101 made of resin that extends in an arc form, multiple blade springs 102 that extend along shoe 101 and are mounted on shoe 101, and a metal base 120 that rotatably supports one end of shoe 101.
A first projecting portion 110 is formed at the tip or free end of shoe 101. Distal groove 111, for housing one end of blade spring 102, is formed in the projecting portion 110. A second projecting portion 112 is formed on the fixed end of shoe 101. Proximal groove 113, for housing the other end of blade spring 102, is formed in the second projecting portion 112.
Attachment holes 121, 122 are formed on base 120. Sliding surface 125, the curved surface 110a of which is formed in projecting portion 110 at the free end of shoe 101, and which can slide in contact, is formed at the tip of base 120. One end of metal pin 130 is fixed at the center of base 120. Pin 130 passes through projecting portion 112 on the fixed end of shoe 101 and a stop ring (not shown) for shoe 101 is mounted on the free end of the shoe. The shoe 101 is thus rotatable around pin 130.
In operation, the chain runs on sliding surface 101a of shoe 101, and a pressure load from blade spring 102 (see FIG. 5) acts on the chain via shoe 101. However, in the conventional blade tensioner, projecting portion 112 on the fixed end of the shoe moves in the direction of arrow a as shoe 101 deforms from a small radius curvature, shown in FIG. 4, to a large radius curvature, as shown in FIG. 5 in shoe 101. As a result, the degree of opening of the proximal groove 113 increases. When the degree of opening of proximal groove 113 changes, the contact position of the end part of blade spring 102 with groove 113 changes and the operation of the blade shoe is adversely affected causing deterioration of the response of the blade tensioner.
Similarly, for projecting portion 110 on the free end of shoe 101, the contact position of the end part of blade spring 102 with distal groove 111 changes when the degree of opening of the open part of distal groove 111 changes due to deformation of shoe 101. Accordingly, the operation of the blade shoe can be adversely affected.
The stiffness of shoe 101 cannot be made high in automotive applications where the temperature change is large, because a large bending stress acts at the portion of shoe 101 shown at the arrow A when shoe 101 deforms.
This invention addresses such conventional problems and offers a blade tensioner that provides reduced deterioration of tensioner response and improves durability.
The blade tensioner of one embodiment of the present invention includes a blade tensioner that applies tension force to a chain. The blade tensioner has a base or bracket and a chain contacting surface over which the chain slides. The chain contacting surface is a surface portion of a resin or plastic shoe having an arcuate shape. The shoe is made of a material which will xe2x80x9ccreep.xe2x80x9d xe2x80x9cCreepxe2x80x9d is the term used in the art to describe the tendency of the shoe to plastically deform in a gradual manner under elevated load and temperature. The fixed or proximal end of the shoe is rotatably mounted to a metal pin. The pin is fixed to the base. The free end or distal part of the shoe slides freely on an adjacent slide surface formed on the base. A flat blade spring or multiple blade springs are positioned on the side of the shoe opposite the chain-contacting surface. The springs have ends inserted into grooves, slots or housings formed in the ends of the shoe. The proximal groove which receives the blade springs in the fixed end of the shoe extends longitudinally toward the tip of the fixed end of the shoe beyond the point where the pin passes through the shoe.
The blade tensioner of a second embodiment includes a blade tensioner to apply tension force to a chain. The blade tensioner is mounted to a base and has a chain sliding surface over which the chain slides. The sliding surface forms a portion of a shoe and has an arcuate shape. The free end of the shoe slides on a slide surface formed in the base. The fixed end of the shoe is mounted rotatably around a metal pin that is fixed to the base. The shoe is kept under load by a blade spring, the ends of which are inserted in a proximal and distal groove formed in the fixed end and the free end of the blade shoe respectively. The distal groove on the free end of the shoe extends longitudinally toward the tip of the free end of the shoe beyond the contact point between the free end of the shoe and the sliding surface of the base.
The blade tensioner of a third embodiment has blade springs whose ends contact a side of the proximal groove at a point which is located longitudinally beyond the attachment position of the pin in a direction toward the tip of the fixed end of the shoe.
The blade tensioner of a fourth embodiment has blade springs whose ends contact a side of the distal groove at a point which is located longitudinally beyond the contact point between the free end of the shoe and the sliding surface of the base.
The blade tensioner of a fifth embodiment, has a concave relief portion or channel formed in the proximal and distal grooves for preventing contact between the blade spring ends and the shoe.
The blade tensioner of a sixth embodiment has a concave space or opening that extends across the width or transverse direction of the blade shoe formed in the fixed and the free ends of the shoe. The concave space may be filled with fiber-reinforced resin.
The blade tensioner of a seventh embodiment has a guide portion that guides the free end of the blade shoe on the sliding surface. The guide portion extends from the edges of the sliding surface of the base. The guide part is provided on both sides in the width direction of the sliding surface and has convex curved members adjacent the blade shoe.
In the present invention, in one or more embodiments, the proximal groove on the fixed end of the blade shoe opens past the pin attachment point and extends further toward the tip of the fixed end of the shoe. Thereby, the degree of opening of the groove opening does not change greatly when the blade shoe deforms and, as a result, the change of the contact point between the groove and the end of the blade spring is reduced. Furthermore, deterioration of the response of the blade tensioner is reduced in this manner. In this case, generation of excessive bending stress in the blade shoe is prevented so that the durability of the blade tensioner is improved.
As for the distal groove on the free end of the blade shoe, it is also preferred that it extends past the contact point between the free end of the shoe and sliding surface or face on the base and extends further in a longitudinally outward direction. In this case, the change of the contact point between the tip of the blade spring and groove is reduced even when the degree of groove opening changes, so that an adverse effect on the operation of the blade shoe is reduced and deterioration of the response of the blade tensioner is reduced.
It is preferable that the contact point of the blade spring with the groove in the fixed end of the shoe is closer to the tip of the fixed end than the pin attachment point. In this case, opening of the groove on the fixed end of the blade shoe can be reduced or eliminated.
In addition, it is preferable, in the distal groove on the free end of the blade shoe, that the contact point between the blade spring and free end is located further toward the tip of the free end of the shoe than the contact point between the free end of the shoe and the sliding surface of the base. In this case, opening of the distal groove can be reduced or eliminated when the blade shoe deforms.
It is preferable to have a relief point or concavity formed in the shoe adjacent the ends of the blade springs. The concavity is a concave channel formed transversely across the grooves in both ends of the shoe. This concave relief channel prevents interference of the end of the blade spring with the blade shoe and defective operation of the blade spring during operation of the tensioner is prevented. Thereby, the deterioration of response of the blade tensioner can be prevented. In addition, in such a case, wear of the contact part of the blade shoe with the end of the blade spring is prevented, so that the durability of the tensioner is improved.
Formation of a concave space or opening that extends in the width direction of the blade shoe at the fixed and free ends is preferable and the weight of the blade shoe is reduced by it and response of the tensioner is improved. In addition, filling of the concave space with fiber-reinforced resin is preferable, and improves the buckling strength of the ends of the blade shoe.
It is preferable to provide a guide element that guides the sliding of the free end blade shoe on the sliding surface. The guide element is attached to the sides to the sliding surface of the base. It is preferable that this guide element be provided on both widthwise sides of the sliding surface and a convex curved surface be formed on the surface of each guide element adjacent the sides of the free end of the shoe. Thereby the sliding resistance between the guide element and the blade shoe is reduced and smooth movement of the blade shoe is realized.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawings and the following brief description thereof, to the detailed description of the preferred embodiments of the invention and to the appended claims.